There is a conventional optical analyzer which guides light from a light source to a measurement cell by an optical fiber and guides the light, which has passed through the measurement cell, to a spectroscope by the optical fiber, as shown in FIG. 6. Then in this configuration, by light path switching means having a reflective mirror provided between the optical fiber, the light source, and the spectroscope, switching is performed between a light path A introducing the light from the light source to the measurement cell via the optical fiber and a light path B guiding the light from the light source to the spectroscope not via the optical fiber.
Then performed in this optical analyzer are: a light source light volume calibration in which a variation in light volume of the light source is regularly calculated with the light path B, and an optical system light volume calibration in which a calibration fluid with known absorbance is regularly poured into the measurement cell in a state of the light path A to calibrate a variation in light volume of the entire optical system including the optical fiber and the measurement cell.
Here, possible factors in the variation in light volume of the entire optical system calibrated by the aforementioned optical system light volume calibration are: a temperature change of the optical fiber, a state change such as oscillation or curvature change, and state changes such as contamination of the measurement cell and a light path length change. The inventor of this application has found that state changes of the optical fiber and a light a source are more likely to occur than the state change of the measurement cell, and a large portion of the variation in light volume of the entire optical system is attributable to the state changes of the optical fiber and the light source, and the variation in light volume caused by the state changes such as the contamination of the measurement cell and the light path length change is relatively small.
Thus, calibration processing of calibrating the variation in light volume caused by the optical fiber and the light source needs to be performed frequently, but calibration processing of calibrating the variation in light volume caused by the measurement cell does not need to be performed frequently.
However, in the aforementioned optical system light volume calibration, the variation in light volume caused by the optical fiber and the light source and the variation in light volume caused by the measurement cell are calibrated together, and a calibration fluid needs to be stored in the measurement cell in accordance with a frequency of the calibration of the variation in light volume caused by the optical fiber and the light source. This requires frequent calibration processing performed by replacing a liquid sample as contents of the measurement cell with a calibration fluid, resulting in user unfriendliness.
Moreover, there is a configuration such that calibration totally different from the calibration shown in FIG. 6 is performed, and as shown in Patent Literature 1, a sample cell and a calibration cell are arranged in parallel to each other, and an optical fiber as light transmission means is moved to thereby achieve switching between a measurement position in which the sample cell is irradiated with light and a calibration position in which the calibration cell is irradiated with light.
However, with the configuration such that the calibration cell is provided separately from the sample cell, a calibration fluid line for pouring the calibration fluid into this calibration cell is required. With the configuration such that a calibration fluid is temporarily sealed into a calibration cell, the calibration fluid deteriorates, resulting in failure to perform accurate calibration. Moreover, variation attributable to contamination of the measurement cell itself cannot be calibrated, causing a problem in that a measurement error occurs. Furthermore, the configuration in Patent Literature 1, as described above, does not perform the mutually different calibrations, but performs a single calibration in a state in which the optical fiber is at the calibration position.